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Abstract

Immunotherapy using dendritic cells (DC) has shown promising results in clinical trials, but few relevant successes are recorded. Therefore, the choice of an appropriate DC population is critical for the outcome of this treatment. The DC used today in immunotherapy are often matured with a cytokine cocktail consisting of TNF-α, IL-1β, IL-6 and PGE2. These cells have deficits in their cytokine production, and also their migratory capacity in vivo needs improvement. After being introduced to bromelain and the effect it has shown on glioma cells, a curiosity about how it would affect DC maturation awoke. Bromelain is a pineapple stem extract that has been clinically used in adjuvant cancer treatment for a long time. The aim of this study was to analyze the effect of bromelain on DC maturation.
Immature monocyte derived DC were stimulated for 24 h with different concentrations of bromelain and compared to cells stimulated with the cytokine cocktail. The phenotype of the generated cell populations was investigated by flow cytometry. Moreover, the phosphorylation patterns of MAP kinase proteins and AKT, in addition to nuclear RelB expression, were examined by Western blot. The migratory capacity of the generated DC populations was analyzed in a chemotaxis assay toward CCL19, and IL-12p70 production was determined by ELISA. The T cell stimulatory capacity of the generated DC populations was investigated by a mixed lymphocyte reaction (MLR).
Bromelain treated DC showed a concentration dependent upregulation of maturation markers and co-stimulatory molecules. However, they had a less mature phenotype compared to DC stimulated with the cytokine cocktail. Phosphorylation patterns of MAP kinase proteins and AKT obtained from Western blotting indicated that bromelain stimulated DC were more similar to immature cells. Nuclear RelB expression of bromelain stimulated DC was lower compared to cytokine cocktail treated DC but higher compared to immature DC. All bromelain concentrations used in this study resulted in increased IL-12p70 secretion by DC compared to cytokine cocktail treated cells and immature DC. The chemotaxis assay revealed that nearly the same number of DC migrated without a chemokine gradient and the MLR revealed that bromelain stimulated DC can induce proliferation of allogeneic T cells comparable to DC treated with the cytokine cocktail.
Although bromelain stimulated DC seem to be less mature than DC treated with the cytokine cocktail, they did produce more IL-12p70. Since lack of IL-12 secretion is one of the drawbacks of using the cytokine cocktail, bromelain might be used as an additional stimulus, in combination with other stimuli during generation of DC used in immunotherapy.